The monoterpenes are a large family of plant natural products that function as defensive agents, pollination attractants and allelopathic compounds (J. B. Harborne, in J. B. Harborne and F. A. Tomas-Barberan (eds.), Ecological Chemistry and Biochemistry of Plant Terpenoids, Vol. 31, Clarendon Press, Oxford, 1991, pp. 396-426; J. H. Langenheim, J. Chem. Ecol. 20:1223-1280, 1994). Over 500 naturally occurring monoterpenes have been identified (J. Buckingham, Dictionary of Natural Products on CD-ROM, Ver. 6.1, Chapman & Hall, London, 1998), a number of which are of commercial importance as flavors and fragrances, pharmaceuticals, insecticides and synthetic intermediates (D. F. Zinkel and J. Russell (eds.), Naval Stores: Production, Chemistry, Utilization, Pulp Chemical Association, New York, 1989, pp. 477-572; B. M. Lawrence, Perfum. Flavor 17:15-28, 1992; F. A. Dawson, Naval Stores Rev. March/April 1994, pp. 6-12).
The universal precursor of the monoterpenes is geranyl diphosphate (GPP) produced by geranyl diphosphate synthase (GPPS) which catalyzes the condensation of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) to the C10 product (see THE FIGURE). This enzyme is similar to farnesyl diphosphate synthase (FPPS) which condenses two molecules of IPP with DMAPP to form the C15 precursor of the sesquiterpenes and triterpenes, and to geranylgeranyl diphosphate synthase (GGPPS) which condenses three molecules of IPP with DMAPP to form the C20 precursor of diterpenes and tetraterpenes (see THE FIGURE). These enzymes, referred to collectively as short-chain prenyltransferases, function at the branch-points of isoprenoid metabolism and are considered to play a regulatory role in controlling the flux distribution of IPP into the various terpenoid families (J. Gershenzon and R. Croteau, in T. S. Moore, Jr. (ed.), Lipid Metabolism in Plants, CRC Press, Boca Raton, Fla., 1993, pp. 339-388).
Given the importance of GPPS in plant isoprenoid metabolism, there is a continuing need to isolate additional types of GPPS proteins, and nucleic acid molecules that encode GPPS proteins, to facilitate genetic manipulation of plants to optimize, or otherwise alter, plant isoprenoid metabolism. In this regard, an unsuccessful attempt was made to purify a GPPS from A. grandis which resulted in only a 15-fold purification of the enzyme with 88% loss of enzymatic activity. The partially purified enzyme was not visible by SDS-PAGE analysis (D. Tholl et al., Arch. Biochem. Biophys. 386:233-242, 2001).